Foams have a variety of applications. In one instance, radio frequency cables (referred to herein as RF cables) include insulation to improve cable performance. One type of RF cable is coaxial cable which includes insulation between the inner conductor and the outer conductor. In one instance, this insulation is a foam.
In the telecommunications industry, the recent trend is that the data frequency transmitted on RF cables has increased over time. Currently, it is common to transmit data using a frequency of between 2.5 and 2.6 GHz, which corresponds to the 4G spectrum. It is anticipated that frequencies will continue to increase over time.
When transmitting data on an RF cable, the loss-rate of energy is referred to as the dissipation factor (DF). Increasing the porosity of the insulation of the RF cable is one way to reduce DF. Porosity is a measure of the void, or empty spaces, in the insulation, and is generally measured as the ratio of the volume of voids to the total volume of the foam.
One way to reduce DF is to provide an insulator having high porosity, such as one formed from a highly foamed dielectric made with polymer resins which are as pure as possible, wherein the foam includes minimal polar groups attached to the polymer and minimum polar additives.
Foams are typically formed using a blowing agent. The blowing agent serves to form bubbles in the polymeric material. Some blowing agents will leach into the polymeric material and will become impurities in the foam. Some blowing agents have adverse environmental impact, such as halohydrocarbons. Some blowing agents require use of a nucleating agent to expedite bubble formation, and these nucleating agents can become impurities in the foam and can increase the costs of producing the foam.
A foam is desired which has a low DF. Such a foam will preferably have minimal impurities. Such a foam will preferably be compatible with a blowing agent which does not add impurities to the foam and requires little or no nucleating agent.